The maintenance of the transmembrane gradient of monovalent cation (high [K+]i and low (Na+]i) is universal property of all nucleated cells and its dissipation is viewed as a hallmark of necrotic-type cell death (1,2). It was shown that a transient and moderate rise of intracellular Na+ concentration in mitogen-treated cells is involved in rejoining DNA strand breaks preceeding DNA synthesis (3), whereas longterm inversion of the intracellular Na+/K+ ratio blocks macromolecular synthesis and cell cycle progression in the majority of eukaryotic cells studied so far (4-7), including vascular smooth muscle cells (VSMC) (8,9). Much less is known about the role of the trans-membrane gradient of monovalent ions in the triggering and progression of programmed cell death (apoptosis).
Cell shrinkage is one of the initial morphological markers of apoptosis in all types of cells, particularly in VSMC (10). In immune system cells, apoptotic shrinkage is so impressive that the term xe2x80x9cshrinkage-mediated necrosisxe2x80x9d was originally proposed to describe this type of cell death (11), and the striking increase in density of shrunken cells was used to separate intact from apoptotic cells (12,13). In lymphocytes, the apoptotic cell volume decrease is caused by the loss of KCl (14) and a major organic osmolyte, taurine (15), due to the CD95 receptor-mediated activation of Clxe2x88x92 and K+ channels and taurine outward transporter (for recent review, see (16)). However, the involvement of perturbation of intracellular ion composition and ionic strength of cytoplasm in the triggering and development of the apoptotic machinery remains unclear. Recently, it was shown that equimolar substitution of extracellular Na+ by K+ protects Jurkat cells from apoptosis induced by Fas-ligand receptors (14), suggesting that dissipation of K+ gradients plays a role in the triggering of apoptosis in immune system cells. Here, we report that in contrast to Jurkat cells, inversion of the [Na+]i/[K+]i ratio blocks apoptosis of VSMC at a site upstream of caspase-3 independently on transmembrane gradient of monovalent cations and cell volume.
The present invention relates to methods, compositions and uses thereof for inhibiting apoptosis in a cell and/or increasing a cell""s resistance to apoptosis. Preferred cells includes vascular smooth muscle cell (VSMC) and cell from the central nervous system.
More particularly, the invention provides a method for inhibiting apoptosis in a cell, comprising the step of increasing the cell""s intracellular [Na+]/[K+] ratio.
The invention also provides a method for increasing a cell""s resistance to apoptosis comprising the step of increasing the cell""s intracellular [Na+]/[K+ ratio.
The invention further provides methods for inhibiting caspase-3 biological activity in a cell, blocking induced chromatin cleavage in a cell, and preventing DNA laddering in a cell, each of these methods comprising the step of increasing the cell""s intracellular [Na+]/[K+] ratio.
The invention also relates to the use of a compound or a composition that is capable of increasing intracellular [Na+]/[K+] ratio in a cell, for inhibiting apoptosis in a cell or for increasing the cell""s resistance to apoptosis. The compound or the composition may also used for the preparation of a formulation for inhibiting apoptosis in a cell or for increasing a cell""s resistance to apoptosis.
The invention further provides a pharmaceutical composition for inhibiting apoptosis in a cell or for increasing a cell""s resistance to apoptosis, the composition comprising a compound that is capable of increasing a cell intracellular [Na+]/[K+] ratio and a pharmaceutically acceptable carrier or excipient.
The methods and compositions according to the present invention may be particularly useful for the prevention or treatment of numerous pathologies such as angina, myocardial infection, congestive heart failure, dilated cardiopathy, cardiopathy secondary to infarction, neurodegenerative disorder, including dementia and alzheimer.